Image courtesy of Robert Okubo
Mountain gorillas live in home ranges where they eat, sleep, mate and move around. The average size of their home range is about 8 km2 but can be as large as 30 km2 (Fossey 1974).
According to a study by Caro (1976), mountain gorillas do not occupy all parts of their home range equally. There were substantial differences between the silverbacks in the time they spend within their home range and in the way that they moved around the area. Caro found that the availability of food supply was the main factor in the movement of the silverback and the number of feeding areas in a day was directly related to the distance traveled. However, migration routes seemed to be fairly stable over long periods of time (Maple & Hoff, 1982). Although the gorilla’s habitat has an abundance of food, nutritionally important food is localized and seasonal. Another reason for daily movement around the home range is for the gorilla to become familiar with what is around him for protective purposes. The availability of their nest site may also affect their movement. Watts (1994) confirmed that looking for mates, also influences mountain gorilla’s habitat use. Unmated male will expand their territory until it is much larger than their metabolic needs in order to obtain some females (Watts, 1994).
Caro (1976) noted that lone silverback ranges overlap with their parental group ranges.
Dian Fossey (1974) concluded that gorillas move in a circular manner as a defense behavior, trampling the vegetation to discourage other gorillas from getting too close and causing conflict. She also noted that male gorillas never travel too far once they leave their group.
Image courtesy of David Lawson
In her five-year study, Dian Fossey (1974) showed that the presence or absence of other gorilla groups was the strongest factor of the ranging patterns in the group that she observed. When two groups came within 1 km from each other, vocalizations were exchanged. Like Caro, Fossey also showed that the range of the mountain gorillas does not remain constant and new areas are constantly introduced.
The mountain gorillas have very few natural
enemies with their only affective predators being humans. Large carnivores,
such as leopards, tigers and lions
are possible predators of gorillas (Maple 1982). There are several major
factors that present threats to gorillas; there is political pressure to
convert the their habitat into areas for farming and commercial use since
the need for land is increasing in those parts of Africa; they are hunted
by poachers for food and body parts; they are very susceptible to human disease;
and civil war between humans near their habitats has contributed to their
deaths. When gorillas are threatened, usually adult gorillas will defend
others in the group by roaring and beating on their chest with their hands
(www.worldwildlife.org/gorillas/threats.ctn).